2008 michigan academy meeting - holocene alluvial fill in a small

Welcome

Geological Sciences Section

2008 Meeting at Western Michigan University

Michigan Academy of Sciences

Arts, and Letters

Holocene alluvial fill in a small

tributary of the Grand River

Ottawa County, Michigan

Patrick M. Colgan

Grand Valley State University

Allendale, Michigan

Michigan

Ottawa County

10 kilometers N

Study

siteGrand

Rapids

1 km

end

moraine

GVSU

Campus

500 meters

N

Little Mac Ravine

Gra

nd R

iver

100 meters N

alluvial plain

Gra

nd R

iver

ravine head

ravine head

ravine head

alluvial fan

fine silty sand (lacustrine)

diamicton

(basal till)

Marshall Sandstone

~ 480-510 feet

clay, silt and fine sand (lacustrine)ele

vati

on

(ft

)

distance (meters)S N

vertical exaggeration ~16:1

North to South Cross Section across GVSU Campus

diamicton (basal till)?

100 meters

coring

site

GV-2

GV-5

GV-9

N

Environmental geology students in Little Mac Ravine.

Setting up the vibracoring tripod.

Preparing to recover a core

Environmental geology students sampling cores.

Wood in core GV-7 overlying unconformity

up

Unconformity at ~1.85 meters depth in core GV-7

Silty and claygravel

and wood

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 10 20 30 40 50

mass Xlf (x 10-8 m3/kg)

Dep

th (

m)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 5 10 15 20 25

% carbonates

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 5 10 15 20 25

% organic

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0

Lithology

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0

LithologyInterpretation

5070 ± 80 BP

Up

pe

r fi

llL

ow

er

fill

Core GV-2

Depth to unconformity is ~ 2.3 to 2.5 meters

180 ± 40 BP

Downstream Site

coarser

Wood in core GV-2

Radiocarbon age:

5070 ± 80 BP

5920-5720 Cal BP

Interpretation

Core GV-5

Up

pe

r fi

llL

ow

er

fill

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 10 20 30 40 50

mass Xlf (x 10-8 m3/kg)

Dep

th (

m)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 5 10 15 20 25

% carbonates

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 5 10 15

% organic/%moisture

Depth to unconformity is ~ 1.9 meters

Upstream Site

0.0

0.5

1.0

1.5

2.0

2.5

0 10 20 30 40 50

mass Xlf (x 10-8 m3/kg)D

ep

th (

m)

0.0

0.5

1.0

1.5

2.0

2.5

0 5 10 15 20 25

% carbonates

0.0

0.5

1.0

1.5

2.0

2.5

0 5 10 15 20 25

% organic Interpretation

Core GV-9

Up

pe

r fi

llL

ow

er

fill

Depth to unconformity is ~ 1.6 meters

Valley Side Site

Source: Anthony Rodriguez

0.87 meters

Alluvial Fill Properties

• Upper Fill

– Texture is variable

– Organic % is moderate

to high

– Carbonate % is low

– Massive and

laminated fines and

sorted sand and

gravel.

• Lower Fill

– Texture is silt and clay

– Organic % is low to

moderate

– Carbonate % is high

– Mainly massive to

finely laminated.

Radiocarbon Analyses From Alluvial Wood – Little Mac Ravine

Sample core analysis C-14 Age Calibrated Years

Beta-217917 stream C 180 ± 40 BP 290-260 Cal BP upper fill

(GVSU-1) exposure (1660-1680 AD)

wood near GV-1 220-140 Cal BP

(1730-1810 AD)

20-0 Cal BP

(1930-1950)

Beta- 235467 GV-7 C 190 ± 50 BP 310-60 Cal BP upper fill

(GVSU-4) (1640-1890 AD)

Wood 40-0 Cal BP

(1910-1950 AD)

Beta-231594 GV-3 AMS 320 ± 40 BP 480 to 310 Cal BP upper fill

(GVSU-3) (1470-1640 AD)

Wood

Beta-223048 GV-2 C 5070 ± 80 BP 5920-5720 Cal BP lower fill

(GVSU-2) (3960-3770 BC)

Wood

C = Conventional radiocarbon method

AMS = accelerator mass spectrometry method

Conclusions

• At least two alluvial fill units are present.

– Older fill - middle Holocene or older?

– Younger fill - Post-settlement ?

• Younger fill is from 0.5 to 2.5 meters thick

over most of the valley.

• Suggests a large change in sedimentation

rates since settlement.

Acknowledgements

• Thanks to the students in environmental

geology classes who helped with the field

and lab work.

• GVSU Geology students Rhiannon

Mulligan, Sarah Nagorsen and Anthony

Rodriguez who worked on research

projects in past geomorphology classes.